Monday, February 11, 2013

Pheasants and Buzzards: Pt 2

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A few weeks back I posted a piece on the shooting of buzzards and the increased pressure on this species imposed by pheasant rearing landowners and keepers. You may remember that towards the back end of last year the government proposed and then rapidly withdrew a a plan to "sub lethally" control buzzard populations to limit losses of pheasants. Last week I was handed a paper on this subject and I think it makes for interesting reading. Titled "Pheasants, buzzards and trophic cascades." and written by A. C. Lees, Ian Newton and Andrew Balmford it was released about four months ago. I'm not sure where I stand re. copyright but I would like to quote some of this paper.
The Abstract sets out the discussion quite succinctly: " The partial recovery of large birds of prey in lowland Britain has reignited conflicts with game managers and prompted a controversial U.K. government proposal to investigate ways of limiting losses to pheasant shooting operations. Yet best estimates are that buzzards are only a minor source of pheasant mortality - road traffic, for example, is far more important. (How many road kill pheasants do you encounter on an average rural drive?) Moreover, because there are often large numbers of nonbreeding buzzards, local control of breeding pairs may lead to their replacement by immigrant buzzards. Most significantly, even if successful, lowering buzzard numbers may directly or indirectly increase the abundance of other medium-sized predators (such as foxes or corvids) which potentially have much greater impacts on pheasant numbers.
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Buzzard Buteo buteo. Guilty of a minor impact on pheasant numbers

When Wildlife Minister Richard Benyon suggested that buzzard numbers could be controlled by nest destruction and translocation the general public and conservation NGOs were not pleased. When he changed his mind (not a U-turn!) it was time for the Countryside Alliance and similar outfits to get annoyed. Between 20 and 35 million pheasants are released by the shooting industry annually, adding to the wild bred stocks. The paper uses a case study of 486 reared pheasants that found that 37.5% were shot and 36% predated or scavenged - principally by foxes. "In this study, raptors were implicated in the deaths of <1% of individuals." Another study in Dorset found that 5-13% of pheasants are killed on the roads.

Conceptual map of interspecific interactions taken from the paper by A.C.Lees et al.

"It is estimated that for each paired buzzard in southern Britain there are up to three additional non-breeding birds (Kenwood et al 2000)" So get rid of your local buzzards and more will soon move in. "Two recently prosecuted Shropshire gamekeepers discovered the extent of such immigration for themselves when they illegally killed over 100 buzzards on one estate in less than six months (Evans 2008)" Over 100 buzzards in less than six months!! Anyone who likes to see a buzzard soaring overhead will no doubt have a strong reaction to news like this.

Ring-necked Pheasant Phasianus colchicus 20 - 35 million released in Britain every year.

An interesting point made by the authors is that : "Although buzzards may have a minor negative impact on game populations by direct predation, this may be more than compensated by buzzard predation on other predators such as corvids which, through nest predation, may have significant impacts on the reproductive success of the wild breeding stock of pheasants." The authors go on to point out that rabbits cause damage reckoned at £180 million annually - and we know what buzzards do to rabbits! Removing buzzards may impose subtle economic penalties on land-owners as well as leading to increased numbers of foxes, which kill at least four times as many pheasants as do buzzards.

Fox Vulpes vulpes. The main predator of Pheasants

The main concern of most people who are not stakeholders in the pheasant business was that the Benyon proposal: " would inadvertently give the greenlight to wider raptor persecution - this at a time when illegal persecution already looks set to drive Hen Harriers Circus cyaneus to extinction in England." I believe that this would definitely be the case. The current laws are already ignored as it is by some.

Common Buzzard Buteo buteo

The paper makes no bones about its findings stating that: "By ignoring their population biology and interaction with other species, ad hoc local control of predators such as buzzards could just as likely exacerbate losses of pheasants as reduce them. In the future, effective game management interventions will require far more rigorous analysis of the ecological, conservation, and economic consequences of maintaining supernormal densities of introduced game species than has been achieved so far."
I'd like to bet that this will not happen. Money talks!
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Common Buzzard Buteo buteo

The paper ends, as expected, with a comprehensive list of references but, it does not give a link to an online version and I only have a hard-copy.